Devices and services that allow seamless hand-off of calls from any network to any other networkWi-Fi at home, cellular, commercial hotspots, enterprise WLANsmay not be widely available for some years. But the idea clearly has appeal, and service providers and handset manufacturers are already taking the first steps to making it happen.

In a recent survey conducted by In-Stat, 84.6 percent of respondents were at least "somewhat interested" in the idea of using a VoWLAN/cellular phone, and half were "very interested" or "extremely interested." Another recent report, from ABI Research, predicts that annual sales of dual-mode phones will likely exceed 100 million units by 2010though the report's author, ABI senior analyst Philip Solis, notes that only 10,000 units had been sold worldwide by the end of 2004.

What's happening todayNTT DoCoMo in Japan is already offering dual-mode phones from NEC that can hand off calls between its cellular network and enterprise customers' WLANs. KT Telecom in Korea is offering a service with hand-off between cellular and hotspots or residential Wi-Fi networks. And British Telecom (BT) has trialed a Motorola dual-mode phone that uses Bluetooth to connect to an enterprise WLAN, and is now reportedly trialing a Wi-Fi version.

In 2003, Avaya, Motorola, and Proxim announced a joint venture to develop Avaya Seamless Communication Solutions, to include both dual-mode handsets from Motorola and technologies for seamlessly handing off calls between cellular and enterprise WLANs. The partners are currently trialing the solution using Motorola's dual-mode CN650 handset, and may offer it commercially as early as the end of this summer, Solis says.

Last week, Calypso Wireless, a Florida-based wireless equipment manufacturer, announced availability of prototypes of its dual-mode Wi-Fi/GSM-GPRS handset, the C1250i. Calypso also has technology for seamlessly handing off between Wi-Fi and cellular networks.

Shifting synergies
The current buzz around dual-mode solutions is partly due to the growing realization among enterprises of the potential synergy between their new IP PBXs and the Wi-Fi WLANs they've been installing. Once you start thinking about providing voice over WLAN (VoWLAN) to provide mobility within a building, it's a short step to realizing the benefits of a converged device that would work as both a VoWLAN phone inside and a cell phone outside. And from there to wanting to be able to hand off calls between WLAN and cell network is an even shorter step.

"Businesses could get away from the need to change wiring when they have to move phones, while at the same time giving better service to employees by offering them a phone they could use anywhere in the building and outside," notes In-Stat principal analyst Allen Nogee.

Interest in dual-mode solutions among enterprise customers, along with a few other developments, has contributed to a tectonic shift in the way various industry players view the dual-mode/seamless hand-off proposition. When the idea was first broached a few years ago, mobile carriers saw it as a threat to their cellular revenues. Customers, they feared, would seek out low-cost Wi-Fi hotspots or corporate WLANs to make calls in order to avoid more expensive cell calls.

That concern has not entirely gone away, says Nogee, but a couple of things have happened to change the mobile carrier view. They now see that dual-mode services could offer a solution to a growing need among their corporate customers for in-building and on-campus coverage. Cellular coverage is poor in many commercial buildings and the only good solution until now, installing pico cells, is so expensive that customers and landlords often balk at it. Cellular carriers face the same problem with consumer customers, many of whom also can't get good coverage in their homes.

Carriers such as NTT DoCoMo, KT and BT may also have simply recognized that the goodwill from responding to customer demands for such converged services and technologies will offset any lost revenues. And now that they're doing it, others will be forced to do it to compete.

If it ain't fixed . . .
In the beginning, though, it was fixed line phone companies that saw a competitive benefit in VoWLAN, Solis says. With the huge drop in the price of cellular minutes, enterprise and consumer customers in increasing numbers were switching to using cellular phones as their only phones because they wanted portability and the convenience of a single phone and number. VoWLAN phones that could be used at home, at hotspots and at the office might keep customers on their wireline networks.

Talk Telecom, an independent telco in Ireland, for example, recently launched a VoWLAN service for its business customers designed to wean employees from making expensive cell phone calls from inside the office. The service, offered through VoIP partner Cicero Networks, doesn't offer hand-offs between WLAN and cellular networks, but users can make calls from a smartphone running Cicero VoIP softwareat about one-fifth the cost of the same call on a cell network.

"Cell phone companies now realize they have to work with landline or VoIP companies so they don't get cut out of the picture completely," says Solis. "They staved off [development of dual-mode solutions] for a whileno handset manufacturer wanted to ruin a good relationship with a cellular company, which is where most of their business comes from, by building [a dual-mode product]. But the cell operators are now asking for it."

Near-term expectations
While various industry players may now have an incentive to explore dual-mode scenarios, the ultimate goal of completely transparent roaming among multiple network domains may take a while to realize. The ABI report paints a tantalizing scenario of a user making a call from his home in the morning using a dual-mode handset. The call initially goes over his Wi-Fi network and onto a wirelinepresumably VoIP network. Then he gets in his car for the drive to work, and the call is handed off to a cellular network. When he arrives at his office, it's handed off again to the office VoWLAN system.

"We're probably nowhere near that scenario right now," says Solis. "The reason is that dual-mode VoWi-Fi/cellular for the enterprise will initially be very different from the kinds of solutions that are being developed for consumer customers."

The Motorola-Proxim-Avaya solution is typical of enterprise-centric approaches, he says. A prime objective is to provide corporate users with all the benefits of the IP PBXtransfers, conferencing, presencewhile they're using a mobile phone either on the WLAN or on the cellular network. A call from a dual-mode device appears to the PBX as a three-way conference call, except two of the conference links are to the same terminal device. Only when the caller moves out of one network's coverage area is the second conference link dropped.

At least initially, the Avaya Seamless Communication Solution won't be able to hand off calls to either hotspots or home networks, Solis says. This is apparently for security and technical reasons. "Although I don't see any reason you couldn't eventually do that as well if you have the right VPN software on the phone," he says.

Resolving complexities
Another impediment to multi-domain roaming is that many companies will opt for 802.11a infrastructure for VoWLAN because of its superior capacity. The Avaya solution supports 11a, b and g, but 11a is the default choice and the Motorola CN650 is an 11a device. Future dual-mode devices may have a/b/g capabilities, though.

Handing off to different providers' hotspots also presents business complications, Nogee points out. "There are a lot of different kinds of hotspots, and some don't even allow the log-in procedure [for VoWLAN phones]," he says. "Also, how do you do the revenue split and who pays for [the technology]?"

Objectives and standards
Consumer-centric solutions, like the one KP is beginning to roll out in Korea, are focused on handing off calls between residential Wi-Fi or hotspot connections and cellular networks. Many will use Unlicensed Mobile Access (UMA), VoWi-Fi/cellular hand-off technology designed to work with GSM/GPRS networks. Motorola recently announced it has begun trials of its UMA solution with seven European wireless operators, including TeliaSonera in Denmark. It's not clear when it will be available commercially.

The holy grail of multi-domain roaming may only come about with the emergence of networks and devices based on the IMS (IP Multimedia Subsystem) specification, Solis says. "When [the standard] moves to [IMS], there will be a higher probability of being able to connect anywhere seamlessly with hand-offs from any network to any other. But [widespread implementation of] IMS is probably ten to 20 years off," he says.

Market pressure might inspire (or force) service and network equipment providers to come up with solutions much sooner, Solis concedes. And disruptive solutions such as putting the Skype soft phone on dual-mode cell phones something Motorola and Kyocera are both working on may also hasten the arrival of multi-domain roaming.

Nobody any more is disputing the potential benefits of having one phone that can be used anywhere, and the benefits for enterprises are particularly tantalizing. Now it's just a question of working out the details of how to do it.

Originally published on .

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